Pen type drug delivery devices have applications where regular injection by persons without formal medical training occurs. This is increasingly common among patients having diabetes or the like. Self-treatment enables such patients to conduct effective management of their disease. The injection pens usually comprise a housing in which a drive mechanism is located. Some kinds of drug delivery devices also comprise a compartment to accommodate a cartridge in which the medicament is received. By means of the drive mechanism, a bung in the cartridge is displaced such that the medicament accommodated therein is dispensed normally through a needle.
Prior to injection, the required dose of the medicament is set by means of a dose setting mechanism. Common designs of dose setting mechanisms comprise a number of tubular or sleeve-like elements such as a dose dial sleeve, a number or dose indicating sleeve, a drive sleeve or a ratchet sleeve that extends in a longitudinal direction from a proximal end to a distal (injecting) end of the drug delivery device. Such sleeves are often accommodated within and connected to each other.
One alternative of dose setting mechanism includes a dose selector or dose dial element that charges a torsion spring by rotation, wherein one end of this spring is rotationally fixed to the dose selector. For an audible signal during dose setting, a ratchet sleeve is connected with the dose selector and is rotated in a first direction. For dose cancellation or dose reduction, the ratchet sleeve is rotated in the opposite direction. During dose setting or dose cancellation, the ratchet produces an audible and tactile click sound by flexible arms of the ratchet snapping over corresponding counterparts located in or at the housing, e.g. ratchet teeth, which is detectable by the human ear. The flexible arm and the corresponding counterpart are called ratchet element in the following. However, the sound produced is in some cases experienced as unpleasant for the user and is interpreted as improper functioning of the device.
In document WO 2011/068531 A1, a leadscrew is rotationally restrained in a passage of a driver. The driver has flexible legs to reduce play between mating cross sections of the leadscrew and the passage to improve dose accuracy. The flexible legs are exclusively provided for guiding the lead screw. A leadscrew brake accommodates the leadscrew such that relative rotation is prevented. A ratchet mechanism between the leadscrew and the body produces a click-sound during dose delivery. By rotation of a dose set knob, the dose set knob screws out of the housing and carries a setback element in the same direction with a ratchet located therebetween, which produces a click-sound during dose setting. The setback element is rotationally fixed to a driver which is moved axially by stop member relative to the leadscrew but does not rotate. Vibrations that emerge from the dose setting mechanism during dose setting produce uncomfortable chatter sound when there is play between the setback element and the driver.
In the injection device described in US 2011/0054412 A1, a traveler is provided between a coupling sleeve and a threaded sleeve and engages the threaded sleeve via a thread. A ratchet is provided between the housing and a dose setting button. The housing surrounds the threaded sleeve, wherein the threaded sleeve may rotate relative to the housing. The traveler interconnects the coupling sleeve and the threaded sleeve and due to the thread engagement, the traveler and threaded sleeve can rotate relative to each other. None of the threaded sleeve or the coupling sleeve has a ratchet element or is directly connected to a ratchet element so that vibration excitations resulting from the ratchet are not directly induced into one of the components.
In EP 2 060 288 A1, a spring is arranged between an outer control element and an item, in which the spring is retained. The spring is arranged such as to be elastically deformed when the control element is rotated relative to the outer control element and has three salients which provide stable and defined positions of the control element. Rotation of the outer control element relative to the item is essential to create a restoring force.
The drive assembly described in WO 2011/154483 A1 comprises a sleeve arrangement with a housing part, a first and a second drive part located therebetween. An elastic spring provides a separating force acting on the drive parts. The spring is part of a uni-directional clutch mechanism, which only acts in axial direction. The coupling members are arranged such that the produce a click-sound. Vibrations can directly be induced into inner sleeve arrangement as the spring provides no compensation.
In WO 88/08725 A1 an elastic sealing ring is provided between the left end of an outer housing and an attachment sleeve serving as a sliding coupling. The attachment sleeve is fixedly connected to a ratchet with a ratchet arm, which interacts with recesses on the outer surface of an adjusting sleeve. Principally, the elastic sealing ring may absorb vibrations, but it is outside a vibration transmission path that runs through the dose setting mechanism.